The present invention relates to stable suspensions of inorganic fillers in polyhydroxyl compounds which are suitable for the production of polyurethanes and to the use thereof for the production of polyurethane resins.
The combination of organic and inorganic raw materials to form a composite material has been known industrially for a long time, for example, when filling rubbers or thermoplastics with inorganic fillers, pigmenting lacquers with inorganic pigments or producing molded plastics material.
In contrast to the above-mentioned rubbers, thermoplastics or molded plastics which are essentially solids and in which the fillers are substantially unchanged in their distribution after incorporation, the polyols generally used in polyurethane chemistry are liquid substances which are only converted into solids or rubbery products after reaction with polyisocyanates.
Inorganic fillers usually have specific gravities above two while the specific gravities of the polyols are generally around one. There is thus such a large difference between the specific gravities of the two components that suspensions of even very finely ground inorganic pigments deposit sediments in the polyols after a certain period. This is particularly true when the polyols have the relatively low viscosities generally required in practice for processing.
This problem represents a considerable obstacle when using inorganic fillers in polyurethane chemistry. Understandably, it is desirable to have such suspensions in a form which is storage stable thus making an additional mixing process for homogenizing the suspensions during storage or before use unnecessary.
An object of the present invention is therefore to prepare storage stable suspensions of inorganic fillers in polyols of the type used in the production of polyurethanes. This object could be achieved in accordance with the teachings of U.S. patent application Ser. No. 856,075 filed on Nov. 30, 1977 by dispersing the inorganic fillers in specific polyhydroxyl compounds containing carboxyl groups, described in more detail below and by optionally diluting the suspensions thus formed with other polyhydroxyl compounds. Polyhydroxyl compounds containing carboxyl groups may be produced simultaneously with the dispersing process in this case. During further processing by this method, it was found that the carboxyl group content could lead to turbulence if the suspensions produced in this way were to be converted into polyurethanes.
However, it has now been surprisingly found that stable and undisturbed suspensions which may be converted into polyurethanes are also formed if the carboxyl groups are completely or partially neutralized by organic or inorganic bases.